Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.376

0.4

0.67

2. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

3. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

3.33

2.33

1.33

4. The domestic refrigerator uses following type of compressor

Centrifugal

Piston type reciprocating

Axial

Miniature sealed unit

5. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Receiver and evaporator

Evaporator and compressor

Compressor and condenser

6. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Brine

Freon

Carbon dioxide

7. Freon group of refrigerants are

Toxic

Non-inflammable and toxic

Inflammable

Nontoxic and non-inflammable

8. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

9. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Super-cooling

Sub-cooling or under-cooling

Normal cooling

10. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant pressure

Takes place at constant temperature

Takes place at constant entropy

Involves no change in volume

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11. In a lithium bromide absorption refrigeration system

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

12. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

13. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Rankine

Reversed Carnot

Carnot

14. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Equally

Less

15. Critical temperature is the temperature above which

Water will evaporate

A gas will immediately liquefy

A gas will never liquefy

Water will never evaporate

16. The freezing point of sulphur dioxide is

-77.7°C

-56.6°C

-75.2°C

-135.8°C

17. The minimum temperature to which water can be cooled in a cooling tower is

Wet bulb temperature of air

Ambient air temperature

Dry bulb temperature of air

Dew point temperature of air

18. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Relative humidity

Dew point temperature

Dry bulb temperature

19. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

15 bar

2 bar

30 bar

20. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Absorber

Evaporator

Condenser

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21. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Detect liquid in vapour

22. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

2.15

5.12

23. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Saturated liquid

Wet vapour

Superheated vapour

24. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

25. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

1: 1

9: 1

1: 3

26. Rating of a domestic refrigerator is of the order of

10 tons

40 tons

0.1 ton

5 tons

27. Which of the following cycles uses air as the refrigerant?

Ericson

Bell Coleman

Carnot

Stirling

28. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

Near critical temperature of refrigerant

Much below critical temperature

At critical Temperature

29. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

30. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

None of these

Positive

Zero

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31. Most thermostatic expansion valves are set for a superheat of

10°C

15°C

20°C

5°C

32. The boiling point of ammonia is

-10.5°C

-33.3°C

-30°C

-77.7°C

33. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Same

Less

34. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Condenser tubes

Refrigerant cooling tubes

Evaporator tubes

35. Which of the following is not a desirable property of a refrigerant?

Large latent heat

Low boiling point

High risibility with oil

Good electrical conductor

36. A bootstrap air cooling system has

Two heat exchangers

Four heat exchangers

Three heat exchangers

One heat exchanger

37. For obtaining high COP, the pressure range of compressor should be

Optimum

Any value

Low

High

38. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

None of the above

Ensures the evaporator completely filled with refrigerant of the load

39. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Always less than unity

Always more than unity

Equal to unity

40. The capillary tube, as an expansion device, is used in

All of these

Water coolers

Room air conditioners

Domestic refrigerators

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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